sub isExe {
  my $exe = shift;
  my @paths = split /;/, $ENV{PATH};
  foreach my $path (@paths) {
    return 1 if -x $path/$exe;
  }
  return 0;
}

##</code><code>##

if (isExe("tail.exe")) {
  print "tail.exe is in my PATH.\n"
}